D

D channel

Stands for delta channel and is a 16Kbps circuit-switched channel. Used to manage control signals.

daisy chain

To connect a series of devices, one after the other. When signals are transmitted on a daisy chain, they go to the first device, then to the second, and so on, until termination is reached.

database server

A type of computer that maintains information records that can be added, deleted, changed, or searched. Database servers play a major role in most companies and on the Internet.

defragmentation

The reorganization of data on a hard disk to optimize performance.

demodulate

To convert an analog signal back to digital data. This is typically done on the receiving end of a computer transmission using standard phone service.

deny

To prevent a user from using other permissions to access a resource. It is far stronger in its effects than simply not giving them permissions.

dialog control

Manages the dialog between the sender and receiver. It consists of managing the transfer of data, determining whether an acknowledgment is required, and determining the appropriate responses to the sender.

differential backup

Uses the archive bit to determine which files have changed since the last normal backup. Files that have changed are backed up. The archive bit is not reset until the next normal backup. If you have to restore data, you need only your last full backup and your last differential tape.

Digital Subscriber Line (DSL)

A digital signaling method used to transmit data over regular phone lines at speeds up to 6Mbps. DSL uses Asynchronous Transfer Mode to pass data in fixed-size cells.

digital videodisc or digital versatile disc (DVD)

Based on the same technology as the CD-ROM, DVDs use a much smaller laser and are able to copy many times more the amount of data. DVDs can hold at least 4.7GB of data and as much as 8.5GB.

DIN

Deutsch Industrie Norm-a German standards organization.

direct memory access (DMA)

DMA enables a device to transfer data directly to RAM without using the attention of the processor for the entire transfer period. The result is a faster and more direct method of data transfer.

directory services model

Uses a hierarchical database to logically organize the network resources. This model scales well to small, medium, or large enterprise networks.

disk controller

Manages floppy and hard disks. It can be a separate piece of hardware, or it can be integrated with the hard drive.

disk partitioning

The process of creating logical disks from a physical disk. You can then format the logical disks and use them to store data.

distributed processing

Sharing the task of processing instructions between a server and a client CPU.

domain model

Logically groups computers, users, and groups into a domain. Users log on to the domain and have access to any resources within the domain to which their user account has permission.

Domain Name System (DNS)

A system that resolves domain names to IP addresses by using a domain name database.

DOS

An operating system developed by Microsoft. DOS predominantly uses command lines to manage the operating system, applications, and files.

DOS shell

The name that is used to describe the software that makes up the DOS user interface.

DOSKEY

A DOS utility that enables the user to customize settings for DOS and add key commands for DOS.

dot pitch

Measures the distance, in millimeters, between two dots of the same color on the monitor.

drivers

Software that shows a particular operating system (Windows 2000, for instance) how to access and interact properly with a specific device (an HP Color LaserJet 4000, for instance). Each piece of hardware therefore may require a different driver for every operating system it is installed in.

dual in-line package (DIP) switches

A set of tiny switches attached to a circuit board that are manually configured to alter the function of a chip for a specific computer or application.

dual-boot

Having two or more operating systems on your computer. At system startup, you can select which operating system you will boot.

Dynamic Host Configuration Protocol (DHCP)

Automates the assignment of IP configuration information.

Dynamic Host Configuration Protocol (DHCP) server

Automates the assignment of IP configurations.